The invention relates to a catching and holding apparatus for the catching-side weft thread end and to a weaving machine comprising a catching and holding apparatus of this kind. Furthermore, the invention relates to a method for the holding and the stretching of the weft thread end and for the transporting away of the severed weft thread end.
In weaving machines, in particular air jet weaving machines, the catching-side ends of inserted weft threads are stretched and held by means of a catching and holding nozzle until the weft thread is beat up and/or the ends are severed. Conventional catching and holding nozzles are therefore frequently also designated as stretching nozzles. In a nozzle of this kind the weft thread ends are engaged by a nozzle jet and led into an opening of a catching tube or passage and held there through the air flow of the nozzle jet.
In the specification of U.S. Pat. No. 4,465,110 a stretching nozzle is described which is arranged at the catching-side end of a reed of an air jet weaving machine. The stretching nozzle comprises a carrier with a cut-out which forms an extension of the guiding passage in which the weft thread is guided during the insertion, as well as a nozzle and a catching passage, which are arranged perpendicularly to the weft insertion direction and which open into the cut-out at opposite sides. The cross-section of this guide passage necessarily has a certain size, through which a relatively large distance between the outlet opening of the nozzle and the catching opening of the catching passage results. In order to bring the weft thread end reliably into the catching opening, a relatively large pressure is required, which leads to a correspondingly large air consumption.
In general a certain distance must be present in a conventional catching and holding nozzle between the outlet opening of the nozzle and the catching opening of the catching passage due to the spatial and possibly also temporal scattering of the thread position. The greater the distance, the more reliably can the thread be engaged by the nozzle jet. Limits are reached, however, in the enlarging of the distance. A free nozzle jet propagates in the form of a cone with an opening angle of approximately 24°, which means that the greater the distance between the outlet opening of the nozzle and the catching opening of the catching passage is, the larger the catching opening must be. A larger cross-section means however a lower air velocity and consequently a lower force acting on the thread. In order to achieve a sufficiently large force acting on the thread, the entry pressure must be increased correspondingly, which necessarily leads to an increased air consumption. Once the speed of sound is reached, the acting force can no longer be increased.